New chemometric strategies in the spectrophotometric determination of pKa

Abstract

KEYWORDSIn this work, principal component regression and partial least squares regression were used for the estimation of acid dissociation constants through UV-Vis spectrophotometric measurements, considering five well-known acid-base indicators as well as two herbicides as analytes. In each case, an acid-base titration was carried out. Then, the multivariate calibration model was constructed with a few absorption spectra of the series at extreme pH values, to which values of the dissociation fraction (α) of 1 or 0 were assigned, in the case of HA or A species. After that, the prediction step consisted in the estimation of α for the rest of the series. Then, distribution diagrams were built up with α vs pH, to find α = 0.5 where pH = pKa. The results were compared with those obtained through multivariate curve resolutionalternating least squares and program stability quotients from absorbance data (SQUAD), which showed an excellent correspondence. pKa PLS PCR MCR-ALS Spectrophotometry Chemometric strategies

Determination of the Dissociation Constants of 5-Substituted 1H-Tetrazoles and Amino Acids by the Concentration Spectrophotometric Method: A New Approach

“…In most cases, the multiwavelength spectrophotometric pH titration, combined with various approaches to experimental data processing, is used for the determination of p K T . For example, a number of authors used the following approaches and programs: MCR-ALS, PLS, and PCR, SPECFIT and SQUAD, − and so forth. , For the primary experimental data these authors used A (absorbance) – pH dependence, obtained from the spectra of the investigated compound at a constant concentration in a set of buffer solutions with various pH values, at a constant ionic strength. Because of that, the determination accuracy of the dissociation constants comes to depend not only on the selected approach to the processing of spectrophotometric data, but on the errors of pH measurements too.…”

Recent advances in capillary electrophoretic migration techniques for pharmaceutical analysis (2013–2015)

“…Main drawbacks of potentiometric techniques include the requirements to use pure drugs in aqueous buffers . In UV‐VIS spectrophotometry, a drug must contain an UV‐active chromophore close enough to the site of the acid–base function in the molecule and it is assumed that its impurities do not absorb in the UV‐VIS range, since the spectra of impurities can overlap with those corresponding to the solutes of interest .…”

Spectrophotometric Determination of the pKa, Isosbestic Point and Equation of Absorbance vs. pH for a Universal pH Indicator

“…Several groups [3]- [6] have investigated the behaviors of different drugs, including those used against cancer, and the dependence of their behaviors on their pKa values. Novel pKa determination methods that use pH colorimetric indicators have also been reported [7]- [9].…”